It is known in the art that the crosslinking of polymers can improve certain physical properties, such as chemical and solvent resistance, and retention of shape at high temperatures. It is the purpose of this invention to provide a method for the crosslinking of polymers that can normally be crosslinked by free radicals and/or contain aromatic rings, by heating the polymer in the presence of oxygen while the polymer is in contact with a compound containing one or more xanthene groups.
U.S. Pat. No. 4,751,102 describes a composition which is a radiation-cureable ink which contains free radical polymerizable compounds and a cationic dye. One such dye described (at col. 4, lines 30-40) contains a xanthene-like moiety, which however, does not contain a hydrogen atom at the 9-position (infra). Also the polymerization of the monomers takes place upon exposure to radiation, not heat. U.S. Pat. No. 4,801,392 describes a very similar system for use in magnetic recording compositions.
U.S. Pat. No. 4,764,566 describes the crosslinking of polymers containing aromatic nuclei (rings) by incorporating a biphenylene unit into the polymer and subsequently heating the polymer to effect crosslinking. No mention is made of using xanthene groups, and the presence of oxygen is not required. Other variations of using biphenylene units in a similar manner are cited within this patent.